Process of refining phosphatovanadic acids



June 27, 1939. F. c; BOWMAN 2,163,773

PROCESS OF REFINING PHOSPHATOVANADIC ACI'DS Filed Jan. 11, 1931' PHOSFHRTD- SUSPENSION NE UTrmuzcRYsmLuz/ms VANADI'C IN HTIOH CRUDE ACID WATER NH4 V;

80..-100C SLOW s'r'z' ADY AUDIT/0N 4% NH v0 ISEPH RA TING ms 50LVINC1 sEPAR/qrmq COHCEl/TRAF CRUDE CRUDE msoLuBLE ma T0 HOT N v0 HH4 v05 m Pum-nEs snwfin'rmfl ea -oc CRKsnuL/zmq PH mqrmq nnvmq EXPOSURE PURE Pl/RE' PURE To NH; Fumsu NH4 v0 H444 v0, HH4 v0 (OPTIONAL) AMMO/Y/l/M no THEY)? was TE PHOSPHfiTE 1.1 Qua)? I'll/17 "ovum/40 I TO C MER .Bnc K TO FOR RETPEATMENT FER TIL/25F? 0H PROCESS IF VALUE wnnrmrrrs/r INVENTOR. OTHER i Z ATTORNEYS Patented June 27, 1939 PROCESS OF REFINING PHOSPHATO- VANADIC' ACIDS Frederic C. Bowman, Los Angeles, Calif., assignor to A. R. Maas Chemical 00., Los Angeles, Calif., a corporation of California Application January 11, 1937, Serial No. 119,965

5 Claims.

"converted into a marketable product under pres- "ent conditions.

This application is directed particularly to a process of refining the phosphatovanadates as re covered from crude phosphoric acid in the manner set forth in my co-pending application, Serial No. 51,076, filed November 22, 19.35, for Phosphatovanadates and method of recovery of the same, now Patent No. 2,130,579 issued Sept. 20, 1938 although it is not limited in its applicability .;to the particular phosphato vanadates disclosed in my said co-pending application.

In the treatment of crude phosphatovanadate precipitates recovered for example from phosphoric acid including vanadium as disclosed in my co-pending application, it has been found that the reduction of the vanadium content of the phosphatovanadates to a marketable form presents the peculiar problem of purification and recovery wherein problems of an unforeseen character are encountered. These problems arise principally because of the impurities carried with the phosphato-vanadate precipitate.

It is an object of this invention to provide a process for the refinement of phosphatovanadates so as toreduce vanadium contents of the phosphatovanadates to a marketable form such, for

example, as ammonium metavanadate NH4VO2.

I Another, object of this invention is to-provide a process of separating the V205 vanadium pentoxide, from the P205, phosphoric pentoxide, of phosphatovanadic acids.

Another object of this invention is to provide a method of separation of vanadium pentoxide from phosphorous pentoxide by digestion with ammonia.

Another object of this invention is to provide a method of separating vanadium pentoxide from sodium silicofluoride present in crude phosphatovanadic acids through the use of controlled neutralization of the phosphatovanadic acids with ammonia.

Another object of this invention is to provide a method of recovery of vanadium pentoxide from the salts of calcium oxide, magnesium oxide, manganese oxide, aluminum oxide, iron oxide, chromium oxide and titanium oxide and the like, present as impurities in crude phosphatovanadic, acid by neutralization of the crude phosphatovanadic acid with ammonia.

Another object of this invention is to provide a method of recovery of vanadium pentoxide from crude phosphatovanadic acids containing imipurities such as silicofluoride and the oxides of the metals present in the crude phosphatevanadic acid by neutralization of the crude phosphatovanadic acids with an alkali such, for example, as ammonia, ammonium hydroxide.

Other objects .and advantages of this invention it is believed will be apparent from the following detailed description of the preferred embodiment thereof as hereinafter set forth.

The process is illustrated in the accompanying drawing which is a flow sheet illustrating the process embodying my invention.

Phosphatovanadic acid, or phosphatovanadates particularly as recovered from crude phosphoric acid in accordance with. the process as disclosed in my Patent 2,130,579, issued Sept. 20, 1938, includes impurities such as sodium. silicofluoride and the oxides of iron, aluminum, magnesium, manganese, calcium, silica, chromium, titanium, etc., which render the recovery of pure vanadium compounds difi'icult of accomplishment.

I have found that the vanadium may be recovered or refined from such crude phosphatovanadates by the neutralization of a phosphatevanadic acid with an alkali such, for example, as ammonia to remove from the solution thus prepared the impurities such as the iron, aluminum, manganese, calcium, silica and chromium oxides, and to then cool the solution and crystallize therefrom ammonium metavanadate NH4VO3.

I have found that by the use of slow, hot neutralization of the impure phosphatovanadic acid suspension with an alkali such, for example, as ammonia, at such a'rate that the solution never becomes even locally alkaline until the last, enabling me to prepare a filterable mass in that the sodium silicofluoride originally present is con verted to a form which will permit filtering and is not broken down into an unfilterable ,ielly as is the case where fast and immediate neutralization of phosphatovanadic acid is resorted to.

I have also found that slow, hot neutralization of a concentrated suspension of phosphatovanadic acid with ammonia, cooling and separation of the crude ammonium metavanadate enables me to produce as a Icy-product a strong ammonium phosphate liquor of value in the production of fertilizer or the like; furthermore, that dissolving the crude ammonium metavanadate so obtained, filtering, concentrating, cooling and crystallizing yields me an ammonium metavanadate of exceptional purity, wherein the elimination of impurities and particularly of phosphorus pentoxide is complete. In this application the hydrated compounds of vanadium pentoxide and phosphorus pentoxide may be represented by the formula:

Experience has shown that where pure chemicals are utilized, the ratio of 0::y:2 will be 1:1:3 or 1:1:4. There may be several other possible monia would not be so material.

ratios, some of which are disclosed in the chemical literature.

When impure phosphoric acid is used in preparing the phosphatovanadic acid, the theoretical ratios are somewhat distorted. Part of the V205 is replaced by a great variety of other materials which are apparently present in solid solution in the crystals formed. Especially is this noticeable of FezOx, CrzOz, A1203, MnO, NazO, S102, F, CaO, MgO, and TiOz. It is not always possible to determine whether these impurities are present in solid solution or in separate phases. The impurities which are present in variable and sometimes very important amounts are: sodium silicofluoride and calcium sulphate. These impurities are generally present as separate phases and may be recognized through the use of the microscope. They are easily distinguishable under the microscope from the phosphatcvanadic acid crystals which are usually to be seen as bright yellow or orange well formed crystals. Typical analyses of these impure phosphatovanadic acids on an air-dry basis show:

Per cent V205 71346.22 P205 32.5 46.74 Loss on ignition 17.0 -23.2

The process as herein disclosed is applicable to any phosphatovanadic acid and it has been demonstrated to work successfully with acids containing in excess of 30% NazSiFs as an impurity. In giving this percent of NazSiFs it is not meant to imply that this is the limit of the impurity of sodium silicofluoride under which the process is workable as there is apparently no limit in this respect. The following is given as illustrative of the process involving my invention:

Phosphatovanadic acids preferably in the form of wet crystals resulting from the operation of the filtration or centrifuging of the precipitate obtained following the method of recovery of phosphatovanadates as disclosed in my co-pending application are suspended in water sufilcient to give a 30 to 35% suspension by weight. The percentage, however, is not at all critical. The temperature of the water of the suspension should be preferably over 80 C. and is preferably maintained at boiling. With the suspension thus formed, ammonia, preferably as a concentrated ammonia water, is added slowly and steadily at such a rate that the batch does not become alkaline to litmus paper until the end of the reaction. This operation permits the phosphatovanadic acid and sodium silicofluoride to dissolve faster than the ammonia neutralizes them.

In carrying out this process, ammonia may be added rather rapidly at the first, but the rate of addition should be decreased to where the addition is quite slow toward the last of the reaction. The minimum time of addition is believed tobe about an hour, and probably one to three hours of hot digestion should be given afterward to complete the reaction.

If the phosphatovanadic acid were pure, the method of adding ammonia would not be material. If the phcsphatovanadic acid did not contain as an impurity compounds of silica such as sodium silicofluoride, the process of adding am- The acid actually obtained from crude phosphoric acid as dis closed in my co-pending application contains, however, approximately 20% NazSiFe. It is my belief that the controlled addition of ammonia as above set forth avoids the formation of gela tinous silica from the fluosilicate, which would render filtration impossible. Controlled slow addition of the ammonia forms granular easily filterable insolubles having usually the form of the original phosphatovanadate crystals. As a suggested explanation of this phenomenon, it is thought that the calcium oxide of the calcium sulphate present and the FezOs, A1203, etc., of the crude phosphatovanadate form silicates with the silicofiuoride in slightly acid solution. This explanation of this phenomenon is purely theoretical and of course the process embodying my invention is in no way dependant upon this explanation of the phenomena observed in carrying out the process as above described.

The amount of ammonia required to be used is such as to produce a slight excess, or enough to turn litmus paper distinctly blue and so that the solution will continue to smell definitely of ammonia for at least ten minutes after the addition of the last ammonia. It is believed that the end-point is half way between mono and diammonium salts. The reactions that occur are:

The neutralized batch is allowed to cool and crystallize out NHrVOs, preferably for at least 24 hours. Probably a longer period would give slightly better recovery of vanadium. The vanadium is then filtered or centrifuged and washed slightly. Thorough washing is unnecessary because subsequent recrystallization of the ammonium metavanadate removes traces of mother liquor left in this stage. The mother liquor is valuable as it is a rather strong solution of ammonium phosphate. A typical analysis is:

Beaum degrees 15 NI-Iz grams per liter 43.6 P205 do 59.9 V do 3406 V205 per cent 7.7 S102 do 20.97 F do 15.97 P205 do 14.02 Ca do 16.13 Mg do 0.37 Mn do 0.41 AlzQg do 3.4,6 F8203 dO.. 6.7 NH; Considerable From this analysis it will be apparent that the leaching of the ammonium metavanadate was incomplete in this case. The remaining vanadium values may be saved if desired by returning the inadequately leached mud to the phosphoric acid plant for reprecipitation as phosphatovanadic acid.

The filtrate is concentrated to a boiling saturated solution of ammonium metavanadate (NH4VO3) and crystallized by cooling, preferably below 20 C. During the crystallization it is desirable to resort to stirring to avoid scaling of the ammonium metavanadate on the apparatus. It is desirable to allow a period of time of at least 24 hours for carrying out the crystallization.

The ammonium metavanadate is filtered or centrifuged in the usual way and dried. High temperature or long exposure will cause slight loss of ammonia with the resulting yellow coloration of the product. If a pure white product is required, exposure to weak ammonia fumes will prevent yellowing of the product. If the product has yellowed, exposure to Weak ammonia fumes will re-whiten the product if the yellow color is not too pronounced.

Analysis of a finished batch of ammonium metavanadate made in the foregoing preferred. way shows that the product is of chemically pure quality suitable for any use or as the raw material for preparing other vanadium salts.

The phosphorus remaining is in the range of 0.0001% to 0.0002% and the sulphur impurity is of correspondingly low, or even lower, percentage.

Having fully described my invention, it is to be understood that I do not wish to be limited to the details herein set forth, but my invention is of the full scope of the appended claims.

I claim:

1. In a method of separating V205 from P205 of crude phosphatovanadic acids including silicofiuoride as an impurity, the steps of digesting the phosphatovanadic acid with ammonia added to an aqueous suspension of the phosphatovanadic acid at such rate that the aqueous solution of phosphatovanadic acid does not include a material excess of ammonia at any point during the reaction until near the completion thereof, then crystallizing the ammonium vanadate formed and separating it from the solution and redissolving said ammonium vanadate and filtering and recrystallizing to obtain a pure ammonium vanadate.

2. In a method of separating V205 from P205 of crude phosphatovanadic acids, the steps of suspending the crude phosphatovanadic acid in water, adding ammonia thereto to crystallize crude NH4VO3 from the suspension, redissolving the crude NH4VO3 in hot water to separate the insoluble impurities crystallizing the NI-I4VO3 from the solution, leaving the phosphorus in solution as phosphate.

3. In a method of refining crystals of crude phosphatovanadic acid precipitated from crude phosphoric acid, the steps of mixing the crystals with hot water, then adding ammonia to the mixture at such rate that the water does not become substantially alkaline at any time until the reaction nears completion, then crystallizing the ammonium vanadate formed and separating it from the solution, then redissolving said ammonium vanadate and filtering and recrystallizing to obtain a pure ammonium vanadate.

4. In a method of recovery of vanadium. from crude phosphatovanadic acid prepared from crude phosphoric acid, which phosphatovanadic acid contains as impurities either in solid solution or hot water, and then adding ammonia at such rate that the phosphatovanadic acid and silicofiuoride dissolve faster than the ammonia neutralizes them, thus maintaining the solution in a nonalkaline condition until the end, then crystallizing a crude ammonium vanadate and separating it from the solution, then redissolving said ammonium vanadate and filtering and separating a purified vanadium compound from the solution by any of several known methods.

5. In a method of recovery of vanadium from crude phosphatovanadic acid including impurities such as the oxides of iron, chromium, aluminum, manganese, calcium and magnesium, and sodium, silica and fluorine in either solid solution or as separate phases, the steps of suspending the crude phosphatovanadic acid in water, and then adding ammonia thereto at such rate as to dissolve the crude phosphatovanadic acid faster than the ammonia neutralizes the same, thus maintaining the solution in a non-alkaline condition until the end, whereby there is formed ammonium metavanadate, then cooling to crystallize the ammonium metavanadate from solution, leaving the phosphorus in solution as phosphate.

FREDERIC C. BOWMAN. 

